fix(sushi): correct dialog styling and positioning

[sebenns]

Summary

• Fixed dialog token inheritance so host overrides such as --sui-dialog-width and --sui-dialog-radius apply to the native dialog.
• Recalculate positioning and size constraints when the viewport changes, keeping open and dragged dialogs visible.
• Added regression coverage for dialog tokens, viewport resizing, and existing button cursor behavior.

Verification

• npm run verify passed.